I'm not sure what the best one might be for performance but I'd give the following a shot:
PuppyLinux (supposed to be super light weight, probably one of the lightest)
LinuxLite (never used it myself but sounds interesting)
Mint XFCE (I'm a fan of Mint)
Xubuntu or Lubuntu (XFCE and LXDE are light weight)
Look into Universal USB Installer or Linux Live USB creator for making bootable USB sticks for installation.